EGA_VGA.DOC 12/10/90 Compo Software





    EGA & VGA monochrome emulation with AT-SPEED V2.20 and up.

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With AT-SPEED V2.20 the monochrome modes of an EGA or a VGA card can be 
emulated on a high resolution monochrome display SM124.



These screen modes have the following properties:



    EGA monochrome: BIOS Code $09, 640 * 350 pixels, 2 colours.

    VGA monochrome: BIOS Code $11, 640 * 480 pixels, 2 colours.



This favours fast screen output. Also the mouse acts faster with many DOS 
applications like MS Windows 3.0 which will resemble mouse operation with 
ATARI GEM.



To emulate one of these graphic cards you may adjust the graphics emulation to 
EGA or VGA with ATS_INST.PRG.



To display the full height of the screen by scrolling you must press the [(] 
key on the numerical keypad and one of the [down] / [up] cursor keys.

By pressing the [(] key on the numerical keypad and the [i] key you may invert 
the screen.



When problems occur with EGA or VGA emulation this may be the result of:

    -   the complex hardware of any EGA/VGA card. It's not possible to 
        demonstrate all possible properties of these graphic cards.

    -   programs which will predict special hardware (registers for colour, 
        logic or masks) which may result in faulty screen output.

    -   programs which will use extended functions of the complex EGA/VGA 
        BIOS.

    -   programs doesn't use real monochrome screen modes but tries to display 
        only two colours in colour mode.

    -   programs (eg. Windows 3.0) in EGA monochrome mode will display black 
        and white pixels at the bottom border. These programs use the display 
        memory as a data buffer. Because the ST displays its full resolution 
        (400 pixels height) you might see the pixels.



Note:   When you use EGA/VGA the available amount of system memory amount will 
        be decreased from 704 kB to 640 kB RAM.



